https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678
--- Comment #41 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- It's likely that caring about exceptions would actually be worse for optimization than caring about rounding modes (because exceptions mean that floating-point operations can write global state, not just read it). I.e., a proper implementation would also indicate splitting -ftrapping-math into the existing parts relating only to local transformations, and something new for the global effects of operations being considered to write the exception state, and so not be movable past any code that might read it (which includes most function calls, and asms depending on whether they might read the floating-point state register). (There are plenty of local bugs in this area - both in machine-independent optimizations, and in machine-specific code, or libgcc code, that doesn't do the right thing regarding exceptions; lots of thorough tests would be needed to find such places. But in general the local bugs should be individually straightforward to fix in a way that the global issues aren't.) (See discussions on the gcc mailing list in Dec 2012 / Jan 2013 / Feb 2013 for more details in this area.)
